SCLS832B October   2020  – May 2021 SN74HCS138

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     4
    2.     5
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     8
    2.     9
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Operating Characteristics
    8. 6.8 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Balanced CMOS Push-Pull Outputs
      2. 8.3.2 CMOS Schmitt-Trigger Inputs
      3. 8.3.3 Clamp Diode Structure
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Power Considerations
        2. 9.2.1.2 Input Considerations
        3. 9.2.1.3 Output Considerations
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2 Detailed Design Procedure

  1. Add a decoupling capacitor from VCC to GND. The capacitor needs to be placed physically close to the device and electrically close to both the VCC and GND pins. An example layout is shown in the Layout section.
  2. Ensure the capacitive load at the output is ≤ 50 pF. This is not a hard limit, however it will ensure optimal performance. This can be accomplished by providing short, appropriately sized traces from the SN74HCS138 to the receiving device(s).
  3. Ensure the resistive load at the output is larger than (VCC / IO(max)) Ω. This will ensure that the maximum output current from the Absolute Maximum Ratings is not violated. Most CMOS inputs have a resistive load measured in megaohms; much larger than the minimum calculated above.
  4. Thermal issues are rarely a concern for logic gates, however the power consumption and thermal increase can be calculated using the steps provided in the application report, CMOS Power Consumption and Cpd Calculation.